Core Flexure Strength of Five Multi-Layered Chairside Zirconias

Objectives: To examine core biaxial flexure strength of six commercially available chairside dental zirconia materials
Methods: Cylinders with a 14.0 mm diameter from blocks of five chairside zirconias: Katana^TM STML, Katana^TM ONE, CEREC Zirconia Plus, IPS e.max^®ZirCAD MT Multi, and IPS e.max^®ZirCAD Prime Block were milled using a PrograMill PM7. Pre-fired cylinders were cut with a Buehler IsoMet 1000 saw to produce twenty 1.6 mm thick core specimens prefired and 1.2 ± 0.2 mm after-fired. The un-sintered discs were polished through 1200 grit SiC. The zirconia was fired according to the manufacturer's firing parameters in the manufacturer’s recommended furnace. Post-sintering, specimens were polished using a Buehler 15 um diamond embedded plate on a Buehler AutoMet 250 automatic polisher using a load of 80N and rate of 200 rpm for 2 minutes. The disc specimens were loaded in a piston-on-three ball testing fixture detailed in ISO 6872. The specimens were loaded at a loading rate of 1.0 mm/minute.

The biaxial flexure strength values were calculated by:

σ = -0.2387 P(X-Y)/b²

where σ is maximum strength (MPa); P is fracture load (N), X and Y are loading constants derived from loading configuration and Poison’s ratio and b is thickness of specimen.
Results: The means and standard deviations at each layer for the biaxial flexure strengths ( Table 1) were analyzed with ANOVA (α≤0.05) and are presented for each material below:
Conclusions: Within the bounds of this study, the IPS e.max^® ZirCAD Prime block had the highest core strength value followed by IPS e.max^® ZirCAD MT Multi and CEREC Zirconia Plus. The Katana^TM STML had the lowest strength value measured in the study.